Exception in thread “main” java.lang.NoClassDefFoundError: org/openqa/selenium/WebDriver

Firstly, check properly if you have all important dependencies for your program.
Secondly, I had similar error while running maven project:

Caused by: java.lang.NoClassDefFoundError: org/openqa/selenium/JavascriptExecutor

And this problem was because of inappropriate plugin, because I tested different versions of Selenium and it didn’t help me.

So when I changed maven-jar-plugin:

<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>3.1.0</version>
 <configuration>
   <archive>
        <manifest>
             <addClasspath>true</addClasspath>
             <classpathPrefix>lib/</classpathPrefix>
             <mainClass>your_main_class</mainClass>
        </manifest>
   </archive>
 </configuration>
</plugin>

to maven-shade-plugin plugin:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-shade-plugin</artifactId>
    <version>3.0.0</version>
    <executions>
       <execution>
            <phase>package</phase>
            <goals>
               <goal>shade</goal>
            </goals>
            <configuration>
                 <transformers>
                    <transformer 
implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                        <mainClass>your_main_class</mainClass>
                    </transformer>
                 </transformers>
             </configuration>
       </execution>
    </executions>
</plugin>

The issue was gone.
The difference between plugins you can find here.

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In addition, sometimes we upgrade our libraries even with same method name. Due this different in version, we get NoClassDefFoundError or NoSuchMethodError at runtime when one library was not compatible with such an upgrade.

Java build tools and IDEs can also produce dependency reports that tell you which libraries depend on that JAR. Mostly, identifying and upgrading the library that depends on the older JAR resolve the issue.

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To summarize:

• try to change versions of Selenium, if it contains all dependencies;
• try to add necessary dependencies if you don’t have it;
• try to check folder of maven if it has or not what says specific error;
• try to play with plugins if nothing helps above.